There are a number of applications that employ brushless DC motors, and, in many of these applications (i.e., vehicles), there are generally two types of systems: sensorless and sensored. Sensored motors generally employ Hall sensors for rotor position detection, while sensorless, brushless DC motors use the motor as the sensor to detect rotor position. One advantage sensorless motors have is the elimination of hardware components (namely, Hall sensors), which are replaced by software. However, one disadvantage with sensorless motors is that, for speeds below a certain threshold (i.e., at startup), the motor signal is so small that it is not generally detectable. Conventional solutions generally employ open loop control at low speed or during startup, but these open loop controls may not be robust or fast enough for some applications (i.e., vehicles). Therefore, there is a need for improved startup control for a sensorless, brushless DC motor.
Some other conventional systems are: U.S. Pat. No. 7,301,298; and Shao et al., “A Novel Direct Back EMF Detection for Sensorless Brushless DC (BLDC) Motor Drives,” Proc. IEEE APEC, pp. 33-38, 2002.